tests: cp: check -rT does not copy through a symlinked destination

* tests/cp/r-T-symlink.sh: New test.  Ensure cp -rT refuses to copy
a directory over a symlink to a directory, while a trailing slash or
omitting -T copies into what the symlink resolves to.
* tests/local.mk (all_tests): Reference the new test.
https://github.com/uutils/coreutils/pull/14993

Link: https://github.com/coreutils/coreutils/pull/398

tests/cp/r-T-symlink.sh

@@ -0,0 +1,47 @@
+#!/bin/sh
+# Ensure cp -rT doesn't copy through a destination symlink to a directory.
+
+# Copyright (C) 2026 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ cp
+
+mkdir src dir &&
+touch src/file &&
+ln -s dir dst || framework_failure_
+
+# With -T, the symlink itself is the destination and is not replaced.
+returns_ 1 cp -rT src dst 2>err || fail=1
+cat <<\EOF > exp || framework_failure_
+cp: cannot overwrite non-directory 'dst' with directory 'src'
+EOF
+compare exp err || fail=1
+test -h dst || fail=1
+test -e dir/file && fail=1
+
+# With a trailing slash the symlink is followed.
+cp -rT src dst/ || fail=1
+test -f dir/file || fail=1
+rm dir/file || framework_failure_
+
+# Without -T, the copy goes into the directory the symlink resolves to.
+cp -r src/. dst || fail=1
+test -f dir/file || fail=1
+cp -r src dst || fail=1
+test -f dir/src/file || fail=1
+test -h dst || fail=1
+
+Exit $fail

tests/local.mk

@@ -620,6 +620,7 @@ all_tests =					\
   tests/cp/preserve-slink-time.sh		\
   tests/cp/proc-short-read.sh			\
   tests/cp/proc-zero-len.sh			\
+  tests/cp/r-T-symlink.sh			\
   tests/cp/r-vs-symlink.sh			\
   tests/cp/readonly-dir.sh			\
   tests/cp/reflink-auto.sh			\